Cables which contain a large number of electrical conductors require the cutting and clamping techniques to be used on the final cable because it saves costs and time. This technique requires that flat plug connectors be used which comprise one or more rows of contact elements that are arranged adjacent to each other and which are provided with cutting and clamping slots that are open at one side. The individual electrical connectors to be connected are pressed into the matching cutting/clamping slot together with their insulation material. At the same time, the slotted walls cut through the insulation and engage with the electrical conductor. This creates a durable electrical and mechanical connection between the electrical conductor and the matching contact element. Since all electrical conductors can be pressed into their matching cutting/clamping slots at the same time, this connection method constitutes a typical mass connection technique. For example, all 68 contacts of a 68-pole flat plug connector can be contacted in a single step. The time saving potential however applies only if ribbon cables of exact grid dimensions are used. Similar concerns also apply to connectors based on other connection techniques than the cutting/clamping technique. In contrast to round cables, these ribbon cables, however, have the shortcoming that they can be bent in one plane only and there are only very limited electrical shielding possibilities. It is, for instance, very difficult to apply a homogenously dense braided shield around a ribbon cable.
Typically, in order to overcome these problems, round cables have been used which either consisted of ribbon cables or which were provided with pre-harnessed, ribbon-cable-like cable ends.
Cables whose conductors or conductor elements herein defined as insulated wires or stranded wires, coaxial cables or twisted conductor pairs, which have been transformed into round cables by conventional stranding procedures cause problems in the connection to electrical connectors such as when the cutting/clamping technique is used. After the cable jacket and, if necessary, the cable shield and interim covers have been removed, the individual conductors or conductor elements spread apart in a disorganized way without staying within certain grid dimensions. Before they can be connected using the clamping and cutting techniques, the conductors must first be aligned next to each other so that they conform to the grid dimensions of the cutting and clamping slots of the flat plug connector. It is therefore quite common for cable manufacturers to cut the cables to the required lengths and supply them with pre-harnessed ends. For this purpose, the cable jacket insulation material, if any, must first be removed and subsequently the individual conductors must be aligned in parallel to each other at the cable ends and then insulating sleeves of the individual conductors must be thermally glued together or glued in parallel onto a film. One example is shown in U.S. Pat. No. 4,576,662. The disadvantage of this pre-harnessing step at the cable manufacturers is that pre-determined cut-to-size cable lengths must be used. Furthermore, the parallel alignment and bonding of the conductors is very time-consuming and the accuracy of the grid dimensions obtained is not very high. To overcome these problems, round cables formed from a ribbon cable are used.
One variant includes round cable which contains a Z-shaped or similarly folded extruded or laminated ribbon cable. The result is, however, not a truly round cable, but rather a ribbon cable which is less wide, yet thicker than an unfolded ribbon cable. As a consequence, the flex behavior in the different directions varies. Furthermore, the total diameter is larger. The Z-folds bend the ribbon cable and cause local expansions, which in turn change the grid dimensions.
U.S. Pat. No. 5,053,583 relates to a ribbon cable which comprises several cables of different diameters and structures that are embedded in an insulating material and to which a round shape has been imparted by folding and/or winding of the ribbon cable and by surrounding this construction with a cable jacket. As a consequence, an air core remains in the middle of this round cable or the middle is filled with conductors of larger diameters after having been cut off to separate them from the ribbon cable.
In another variant, DE-8322828 UI relating to an extruded or laminated ribbon cable is spirally wound around a carrier element of circular cross-section to produce a round cable. The shortcoming of this method is that the diameter of the round cable is much larger than that of comparable normal round cables. Furthermore, this design causes the cable less flexibility.
Another variant is described in DE-8307764 UI. This round cable is made from an extruded ribbon cable which has been twisted into a round cable shape and around whose circumference a metallic shield was wound which was then surrounded by an insulating outer jacket. This round cable, too, has a larger diameter than a comparable normal round cable. Since the individual conductors were embedded into a single, ribbon-shaped insulation material during the extrusion process, the conductors are much more difficult to displace relative to each other than the independent individual wires of a normal round cable. As a consequence, an air core in the middle of this round cable is virtually unavoidable.
What all round cables made from an extruded or laminated ribbon cable have in common is the fact that no deviations from the predetermined grid dimensions are admissible.
In German Utility Model application, G9113530.6, a round electrical cable is formed when a ribbon cable is twisted into a round shape. The ribbon cable comprises a plurality of electrical conductor elements arranged in parallel and adjacent to each other wherein the conductor elements are attached to each other by means of weaving threads and/or bands.
The diameter of this cable is basically no larger than that of a comparable normal round cable; the flexibility is the same as for a comparable normal round cable; and the grid tolerance is much larger than for a conventional round cable comprising ribbon cables.
In this type of design, the individual conductor elements are not held together by lamination or extrusion but are held together by being woven to form a ribbon cable, resulting in a higher flexibility of the ribbon cable and having much greater freedom for the individual conductor elements to move within the ribbon cable than is achievable with laminated or extruded ribbon cables. The freedom of the individual conductor elements of the woven ribbon cable to move prevents the formation of substantial cavities when the cable is twisted into a round shape and thus minimizes the diameter of the round cable. The weaving together of the ribbon cable prevents high expansion or joint forces while the cable is twisted into its round shape, as occurs with extruded or laminated ribbon cables.
The weaving together of the individual conductor elements to form a single ribbon cable is technically so complex that it is not adequate for some cable types. The usual material for weaving threads or bands is not suitable to influence the electrical properties of the cable, which is frequently desired.
There is a need for a round cable which can be produced from a ribbon cable, which has the benefits of the round cable obtained by weaving and twisting, yet can be produced at less technical expense and allows for a better control of the electrical properties of the round cable.